This present invention relates to an ink supply cartridge for a thermal ink jet printer, and more particularly to an improved means for producing an ink flow passageway between the cartridge and printhead and concurrently providing a seal therebetween.
In existing thermal ink jet printing, the printhead comprises one or more ink filled channels, such as disclosed in U.S. Pat. No. 4,774,530, communicating with a relatively small ink supply chamber, or reservoir, at one end and having an opening at the opposite end, referred to as a nozzle. A thermal energy generator, usually a resistor, is located in each of the channels, a predetermined distance from the nozzles. The resistors are individually addressed with a current pulse to momentarily vaporize the ink and form a bubble which expels an ink droplet. The acceleration of the ink out of the nozzle while the bubble is growing provides the momentum and velocity of the droplet in a substantially straight line direction towards a recording medium, such as paper. Because the droplet of ink is emitted only when the resistor is actuated, this general type of thermal ink jet printing is known as "drop-on-demand" printing.
In current practical embodiments of drop-on-demand thermal ink jet printers, it has been found that the printers work most effectively when the pressure of the ink in the printhead nozzle is kept within a predetermined range of gauge pressures. Specifically, at those times during operation in which an individual nozzle or an entire printhead is not actively emitting a droplet of ink, it is important that a certain negative pressure, or "back pressure," exist in each of the nozzles and, by extension, within the ink supply manifold of the printhead. A discussion of desirable ranges for back pressure in thermal ink jet printing is given in the "Xerox Disclosure Journal," Vol. 16, No. 4, July/August 1991, p. 233. This back pressure is important for practical applications to prevent unintended leakage, or "weeping," of liquid ink out of the nozzles onto the copy surface. Such weeping will obviously have adverse results on copy quality, as liquid ink leaks out of the printhead uncontrollably.
A typical end-user product in this art is a cartridge in the form of a prepackaged, usually disposable, item comprising a sealed container holding a supply of ink and, operatively attached thereto, a printhead having a linear or matrix array of channels. Generally the cartridge may include terminals to interface with the electronic control of the printer; electronic parts in the cartridge itself are associated with the ink channels in the printhead, such as the resistors and any electronic temperature sensors, as well as digital means for converting incoming signals for imagewise operation of the heaters. In one common design of printer, the cartridge is held with the printhead against the sheet on which an image is to be rendered, and is then moved across the sheet periodically, in swaths, to form the image, much like a typewriter. Full-width linear arrays, in which the sheet is moved past a linear array of channels which extends across the full width of the sheet, are also known. Typically, cartridges are purchased as needed by the consumer and used either until the supply of ink is exhausted, or, equally if not more importantly, until the amount of ink in the cartridge becomes insufficient to maintain the back pressure of ink to the printhead within the useful range.
Other considerations are crucial for a practical ink supply as well. The back pressure, for instance, must be maintained at a usable level for as long as possible while there is still a supply of ink in an ink cartridge. Therefore, a cartridge must be so designed as to maintain the back pressure within the usable range for as large a proportion of the total range of ink levels in the cartridge as possible. Failure to maintain back pressure causes the ink remaining in the cartridge to leak out through the printhead or otherwise be wasted.
U.S. Pat. No. 5,233,369 discloses an ink-supply cartridge wherein two chambers are provided, the upper chamber having a capillary foam and the lower chamber substantially filled with ink. The printhead is disposed at a vertical height greater than the top level of the lower chamber. A second capillary foam, disposed along the supply line to the printhead, has a capillarity greater than that of the foam in the upper chamber. In another embodiment, only one chamber, corresponding to the lower chamber in the first embodiment and having no capillary foam therein, is provided.
U.S. Pat. No. 4,771,295 discloses an ink-supply cartridge construction having multiple ink storage compartments. Ink is stored in a medium of reticulated polyurethane foam of controlled porosity and capillarity. The medium empties into ink pipes, which are provided with wire mesh filters for filtering of air bubbles and solid particles from the ink. The foam is also compressed to reduce the pore size therein, thereby reducing the foam thickness while increasing its density; in this way, the capillary force of the foam may be increased.
U.S. Pat. No. 4,791,438 discloses an ink jet pen (ink supply) including a primary ink reservoir and a secondary ink reservoir, with a capillary member forming an ink flow path between them. This capillary member draws ink from the primary reservoir toward the secondary ink reservoir by capillary action as temperature and pressure within the primary reservoir increases. Conversely, when temperature and pressure in the housing decreases, the ink is drawn back toward the primary reservoir.
U.S. Ser. No. 08/151,625, filed Nov. 15, 1993, entitled "Ink Supply Cartridge For An Ink Jet Printer" by Dietl et al. and assigned the same assignee as the present invention, discloses the use of a thin layer of a film forming polymer, such as Mylar.RTM., having a predetermined shape and a slot therethrough, with a thermosetting adhesive layer on both sides to form an ink passageway when positioned over an elongated recess in an external surface of an ink supplying cartridge. The cartridge outlet is connected to the recess, and the printhead is mounted against the film layer in such a manner that the printhead inlet is aligned with the slot in the film layer. The adhesive layer on one side of the film layer bonds the film layer to the cartridge and the adhesive layer on the other side bonds the printhead thereto and concurrently seals the film layer slot to the printhead inlet. Because the adhesive layers are exposed to the ink, the adhesive is a type that is not attacked by the ink.